The invention concerns a method and an apparatus, which, in pressure and vacuum measuring engineering equipment, prevent the intrusion of corrosive or condensable gases, or vapors, into the inside of connected components, and inhibit impurities contained in a gaseous measuring medium, without thereby reducing the function, such as, for instance, the measuring accuracy or the measuring range, of connected components and analyzers.
In manometry, it is known that by means of controlled flow-through throttling of a constant protective gas flow into the measuring lines, the intrusion of corrosive or soiled gases and vapors containing entrained dust and dirt particles into the measuring element can be avoided.
Rinsing of measuring lines for protection against corrosive media and against dust and dirt entry however, requires a steady supply of protective gas, and leads, especially at low pressures, to measuring errors.
For the protection of diaphragm-vacuum measuring instruments, there is further known a gas rinse flange, whereby, via a fine jet, a protective gas current of approximately 200 Pa l/s flows in such a way into the flange interpolated between the measuring instrument and the recipient, that the protective gas stream, in the direction to the recipient, is as great as the occurring diffusional flow of undesired vapors in the opposite direction.
The utilization of a gas rinse flange in the appropriate vacuum range has the disadvantage, however that in addition to the protective gas, a higher suctioning capability of the vacuum pump, for instance of 5 m.sup.3 h.sup.-1 is required for pumping out to approximately 100 Pa. Furthermore, the protection is only effective up to approximately 40 kPa absolute pressure; over and above this limit, the instrument has to be shut off from the apparatus by an additional valve.
For the protection of vacuum analyzers from harmful condensable gases and vapors, there is also known the interpolation of a low-temperature trap, which is filled with liquid nitrogen (freezing pocket, baffle). Interpolated freezing traps in front of the compression vacuum measuring instruments should also prevent the intrusion of mercury vapor out of the measuring instrument itself and into the recipient.
When freezing traps are used, in addition to the required constant monitoring and replenishing with the expensive liquid nitrogen, there also have to be calculated additional measuring errors, because only the portion of the non-condensable gases and vapors of the measuring media are measured.
Furthermore, by using compression-vacuum measuring instruments at low absolute pressures, values reduced by about 40% are measured, because the mercury vapor which leaks out of the measuring liquid and flows into the cooling trap repels a portion of the gas molecules from the recipient, which thus escapes measuring.
It has been attempted to reduce the diffusion of propellent vapors into the mechanical prevacuum pump in diffusion pumps of high-vacuum engineering by interpolating, for instance, water cooled refrigeration sections or refrigeration traps. But this has proved itself insufficiently effective, for instance in pumping stations for the evacuation of picture tube flasks.
It is also known that intrusion of mechanical impurities into analyzers, for instance during intake of atmospheric air, is usually reduced by filters made of fine meshed metal sieves, or sintered pore filters (bronze or glass) or felt, whereas for protection against vapor deposits on cold cathode-vacuum analyzers, deflection plates are used, which prevent the rectilinear diffusion of vapor particles, and which should protect against dust and dirt entry.
The pore filters, however, can only protect the analyzers against coarse impurities, and have to be changed or cleaned after prolonged usage, because otherwise the measurements will be inaccurate, due to the strong throttling of the line cross section.
Deflection plates for protection against vapor deposits are also only of limited effectiveness, mainly because they do not reduce the necessity of frequent cleaning of cold cathode-vacuum analyzers.